The use of high performance thermoplastic composite (HPPC) sheet materials in many automotive applications has increased due to the characteristics of the HPPC material. These sheet materials are an improvement over conventional composite sheet materials, which were generally made to include glass or carbon fibers in a matrix of a thermoset, an epoxy or a polyester material.
HPPC materials, conversely, use a thermoplastic base rather than a thermoset, with continuous glass fibers as the stiffening material. These materials do not sag as compared to standard composite sheet materials and generally provide the same stiffness as a piece of aluminum sheet metal.
However, HPPC sheet materials generally do not provide very good aesthetic properties on their surface, which limits their use in many applications wherein the aesthetics of the piece are as important as their functionality, such as for body panels. One solution to obtain a class A surface for an HPPC sheet material has been to cover the HPPC sheet materials with a thermoplastic foil. However, in these embodiments, the unidirectional glass fiber in the HPPC is visible in high gloss applications. This is caused by the different thermal expansions between the glass matrix and thermoplastic material in between. Painting the part still does not remedy these problems.
Another solution is combining a HPPC sheet material, such as Azdel SuperLight (SL), with thin (0.1-0.3 mm) aluminum foils. In these embodiments, the outer surface has similar thermal expansion as the glass matrix, hence these products can provide a class A finish. The drawbacks of these composite sheet materials are that these thin foils are easily punctured with sharp objects making them unsuitable for many the applications where this is likely to happen. Also dent resistance is likely to be reduced.
Accordingly, it would be beneficial to provide a stiff, lightweight composite sheet material that has a better surface finish than prior art composite sheet materials without one or more of the problems associated with prior art solutions. It would also be beneficial to provide a method of making a stiff, lightweight composite sheet material that has a better surface finish than prior art composite sheet materials.